U.S. patent number 6,808,466 [Application Number 10/387,912] was granted by the patent office on 2004-10-26 for chain tensioner.
This patent grant is currently assigned to Tsubakimoto Chain Co.. Invention is credited to Hiroshi Hashimoto, Osamu Yoshida.
United States Patent |
6,808,466 |
Yoshida , et al. |
October 26, 2004 |
Chain tensioner
Abstract
In a chain tensioner having a plunger biased to protrude from a
housing by a spring, a pair of wedge-shaped cams are received in
tapered recesses in the end of the housing, cooperate with racks
formed on opposite sides of the plunger, and are urged against
oblique seats formed by the tapered recesses by a biasing spring.
The cams and racks produce a ratcheting action maintaining chain
tension by preventing retracting movement of the plunger. The cams
and racks disperse the load imparted to the plunger by the chain,
and reduce localized wear, allowing the housing to be made from a
light weight material such as aluminum. Accuracy requirements
associated with conventional pawl-type ratcheting tensioners are
avoided.
Inventors: |
Yoshida; Osamu (Osaka,
JP), Hashimoto; Hiroshi (Osaka, JP) |
Assignee: |
Tsubakimoto Chain Co. (Osaka,
JP)
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Family
ID: |
19193509 |
Appl.
No.: |
10/387,912 |
Filed: |
March 13, 2003 |
Foreign Application Priority Data
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Mar 28, 2002 [JP] |
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2002-091895 |
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Current U.S.
Class: |
474/110;
474/117 |
Current CPC
Class: |
F16H
7/0848 (20130101); F16H 2007/0806 (20130101); F16H
2007/0859 (20130101); F16H 2007/0853 (20130101); F16H
2007/0812 (20130101) |
Current International
Class: |
F16H
7/08 (20060101); E16H 007/08 () |
Field of
Search: |
;474/101,109,110,111,113,117,135,137,140 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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8-93867 |
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Apr 1996 |
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JP |
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2003-184970 |
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Jul 2003 |
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JP |
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Primary Examiner: Bucci; David A.
Assistant Examiner: Johnson; Vicky A.
Attorney, Agent or Firm: Howson and Howson
Claims
We claim:
1. A chain tensioner comprising: a housing having a
plunger-receiving hole, said hole having an opening; a plunger
slidably fitting into said plunger-receiving hole and protruding
from the opening thereof in a protruding direction; and a first
spring biasing said plunger in said protruding direction;
wherein the improvement comprises: toothed racks formed on opposite
sides of said plunger; a pair of wedge-shaped cams on opposite
sides of said plunger, each said cam being disposed adjacent one of
the respective toothed racks, each said cam having teeth lockingly
engageable with teeth of the adjacent one of said racks to prevent
retracting movement of the plunger relative to said cams, and each
cam having an oblique surface for engagement with a seat, said
oblique surface of each cam facing outwardly away from said
plunger, the shape of each said oblique surface being such that the
oblique surface has an outer end disposed farther along said
protruding direction than an inner end thereof; a pair of oblique
cam seats formed in said housing on opposite sides of said plunger,
the oblique surfaces of the cams conforming to, and being in
engagement with said oblique cam seats and slidable thereon to an
extent such that the teeth of the cams can be brought into and out
of locking engagement with the teeth of said toothed racks; a
spacer disposed on the housing adjacent said opening; and a second
spring engaged with said spacer and said cams, said second spring
urging said cams in a direction opposite to said protruding
direction whereby the cams are urged into locking engagement with
said toothed racks.
2. A chain tensioner according to claim 1, in which said plunger
and said housing define an oil chamber within said housing, and
including a hydraulic valve mechanism on said housing for allowing
one-way flow of oil from an external supply of oil under pressure
into said oil chamber to apply an additional force biasing said
plunger in the protruding direction.
3. A chain tensioner according to claim 1, in which said plunger is
rotatable in said housing, whereby engagement between said rack and
said wedge-shaped cams can be forcibly released.
4. A chain tensioner according to claim 1, in which the protruding
portion of said plunger has a flange, and in which said first
spring is interposed between said flange and said spacer.
5. A chain tensioner according to claim 4, in which said spacer is
held against the housing by said first spring.
6. A chain tensioner according to claim 1, in which said first
spring is disposed in said plunger-receiving hole and is interposed
between an end of the plunger located within said hole and an end
of said hole.
Description
FIELD OF THE INVENTION
This invention relates to a chain tensioner for maintaining proper
tension in a power transmitting chain. The tensioner has utility,
for example, in maintaining tension in the timing chain of an
internal combustion engine, where the chain transmits power from a
crankshaft sprocket to one or more camshaft sprockets.
BACKGROUND OF THE INVENTION
In a conventional tensioner, a plunger, protruding from a housing,
exerts a force on the back of a pivoted tensioner lever having a
shoe in sliding contact with the slack (return) run of a chain in
order to maintain tension in the chain. The plunger of the
tensioner engages the lever at a location remote from the pivot
axis of the lever.
A conventional ratchet type tensioner 500, as shown in FIGS. 9 and
10, comprises a plunger 510, slidable in a hole 531 formed in a
housing 530. The plunger protrudes from the housing, and is biased
in the protruding direction by a spring 520. A pawl 550, pivotally
supported by a pin 540 on the housing 530, is biased by a spring
560 so that its pawl teeth 551 engage teeth 511 formed on the outer
periphery of the plunger.
When the plunger 510 protrudes from the housing 530 as a result of
loosening of the chain, and is thereafter subjected to an impact
force from the tensioner lever, the ratchet mechanism blocks
retraction of the plunger by engagement of the pawl teeth 551 with
the ratchet teeth 511 on the plunger.
When the ratchet operates to prevent retraction of the plunger, the
ratchet pawl 550 applies a sideways force to the plunger, which
results in eccentric loads, indicated by arrows F1 and F2 in FIG.
10, exerted by the plunger on the hole 531. Especially when the
housing 530 is formed of aluminum, these loads can result in
significant localized wear.
In the conventional ratchet-type tensioner 500, when the plunger
510 is subjected to excessive impact force from the tensioner
lever, the impact force is concentrated on the ratchet teeth 511
and the pawl teeth. The impact force produces significant wear of
the tips of these teeth, and failures due to excess wear or
breakage of the teeth can occur.
Furthermore, in the conventional ratchet-type tensioner 500, the
control of tension in a traveling chain depends on engagement
between the ratchet teeth 511 and the pawl teeth 551. To attain
smooth engagement of these teeth, high accuracy in the diameter and
mounting position of the pivoting pin 540 are required. Troublesome
problems have been encountered in the production of the pin, and
also in the production of a pawl with an accurately positioned
pin-receiving hole having the proper diameter.
Among the objects of the invention are the solution of the
above-described problems, and the provision of a chain tensioner
which can disperse and reduce the load applied to the plunger,
which exhibits superior wear resistance, and which can reduce the
requirement for high accuracy in production of components and
assembly thereof.
SUMMARY OF THE INVENTION
The chain tensioner in accordance with the invention is similar to
a conventional chain tensioner in that it comprises a housing
having a plunger-receiving hole with an opening, a plunger slidably
fitting into the plunger-receiving hole and protruding from the
opening thereof in a protruding direction, and a spring biasing the
plunger in the protruding direction.
The chain tensioner differs from the conventional chain tensioner
in that it comprises toothed racks formed on opposite sides of the
plunger, and a pair of wedge-shaped cams on opposite sides of the
plunger, each cam being disposed adjacent one of the respective
toothed racks, each the cam having teeth Mockingly engageable with
teeth of the adjacent rack to prevent retracting movement of the
plunger relative to the cams, and each cam having an oblique
surface for engagement with a seat. The oblique surface of each cam
faces outwardly away from the plunger, and the shape of each
oblique surface is such that the oblique surface has an outer end
disposed farther than an inner end thereof along the protruding
direction of the plunger. Oblique cam seats are formed in the
housing on opposite sides of the plunger, and the oblique surfaces
of the cams conform to, and are in engagement with the oblique cam
seats and slidable thereon to an extent such that the teeth of the
cams can be brought into and out of locking engagement with the
teeth of the racks. A spacer is disposed on the housing adjacent
the opening, and a second spring, engaged with the spacer and the
cams, urges the cams in a direction opposite to the protruding
direction of the plunger so that the cams are urged into locking
engagement with the toothed racks.
In a preferred embodiment, the plunger and housing define an oil
chamber within the housing, and a hydraulic valve mechanism is
provided on the housing for allowing one-way flow of oil from an
external supply of oil under pressure into the oil chamber to apply
an additional force biasing the plunger in the protruding
direction.
In a preferred embodiment of the invention the plunger is rotatable
in the housing, so that engagement between the rack and the
wedge-shaped cams can be forcibly released.
If the plunger-biasing spring is interposed between the flange and
the spacer, it is more easily installed, and can be used to hold
the spacer against the housing.
In an alternative embodiment, the plunger-biasing spring is
disposed in the plunger-receiving hole and is interposed between an
end of the plunger located within the hole and an end of the hole.
In this case, the spacer is preferably screwed into housing.
The chain tensioner of the invention may be either the inner
mounting type or an outer mounting type.
The teeth on the plunger racks and the cams can take various forms
so long as they are capable of exhibiting a ratcheting action
allowing the plunger to move in the protruding direction but
preventing retraction thereof. The protrusion biasing spring causes
the plunger to move rapidly in the protruding direction when the
chain becomes loose, thereby reestablishing proper tension.
The cam biasing spring, which is loosely fitted onto the plunger,
biases the wedge-shaped cams against their seats, which, in turn,
exert a radially inward force on the cams so that they are urged
into engagement with the plunger. However, when the plunger moves
in the protruding direction, it draws the cams with it in the
protruding direction, and at the same time its teeth, in
cooperation with the teeth of the cams, urge the cams radially
outwardly, holding the cams against their seats until the teeth
disengage. At the instant when the teeth become disengaged the
plunger will move forward by one tooth of the rack, and the cams
are immediately reengaged with the rack, to prevent retracting
movement of the plunger, and maintaining proper chain tension.
The use of cams on opposite sides of the plunger distributes the
force applied by the chain to the plunger, thereby avoiding
concentrated loads on the housing. Moreover, the cams distribute
the force symmetrically, avoiding eccentric loads as in the case of
the conventional tensioner.
Furthermore, in the chain tensioner according to the invention,
even when the plunger is subjected to excessive impact force from
the chain through a tensioner lever, the plunger is prevented from
retracting so that proper chain tension is maintained.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevational view showing a chain tensioner in
accordance with a first embodiment of the invention installed in an
internal combustion engine to maintain tension in a timing
chain;
FIG. 2 is a partly cut away perspective view of the chain tensioner
shown in FIG. 1;
FIG. 3 is an exploded perspective view of the chain tensioner shown
in FIG. 1;
FIGS. 4(a)-4(c) are sectional views of the chain tensioner shown in
FIG. 1, illustrating stages in the operation thereof;
FIG. 5 is a sectional view illustrating the distribution of load in
the chain tensioner of FIG. 1 when a force is applied to the
plunger;
FIG. 6 is a partly cut away perspective view of a chain tensioner
in accordance with a second embodiment of the invention;
FIG. 7 is a cross-sectional view of the chain tensioner shown in
FIG. 6;
FIG. 8 is a schematic view showing a chain tensioner in accordance
with a third embodiment of the invention, illustrating the
relationship of the tensioner with a tensioner lever and a
transmission chain;
FIG. 9 is an sectional view of a conventional ratchet type
tensioner; and
FIG. 10 an elevational view showing a conventional chain tensioner
installed in an internal combustion engine to maintain tension in a
timing chain.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The chain tensioner 100 of the first embodiment, illustrated in
FIGS. 1-5, is an "outer attachment" type chain tensioner, which is
attached from the outside of an engine. The tensioner is used to
suppress the vibration generated as a timing chain TC travels over
a crankshaft sprocket S1 and camshaft sprockets S2 of an engine and
also to maintain proper tension in the chain.
In the chain tensioner 100, a spring-biased cylindrical plunger 120
protrudes toward the timing chain TC, which travels past a
tensioner housing 110 attached to a wall E of the engine block
wall. The tensioner plunger presses against the back surface of a
tensioner lever TL, which is pivoted on the engine block, so that a
shoe surface of the tensioner lever TL is held in sliding contact
with the slack side of the timing chain TC to maintain tension in
the timing chain.
A tensioner guide TG, fixed to the engine block, guides the timing
chain TC so that side run-out of the timing chain TC is
prevented.
As shown in FIGS. 2 to 4, the chain tensioner 100 includes a
housing 110 having a plunger-receiving hole 111 into which a
plunger 120 is inserted. The plunger protrudes from the hole, and a
spring 130, which surrounds the plunger and is in engagement with a
flange formed at the outer end of the plunger, biases the plunger
120 in the protruding direction. Two wedge-shaped cams, which are
in the nature of cam chips, are engaged respectively with two
toothed racks separately formed on opposite sides of the plunger
120. The wedge-shaped cams are disposed in tapered recesses formed
in the front end of the housing on opposite sides of the front
opening of the plunger-receiving hole 111. These cams are in
sliding engagement with obliquely tapered cam seats 112 constituted
by walls of the recesses, as shown in FIG. 2. A cam biasing spring
150 surrounds the plunger with clearance, biasing the cams 140
against the obliquely tapered seats so that the cams are urged
radially inwardly into engagement with the plunger. The biasing
spring 150 is held between the cams and a spacer 160, which is held
against the end of the housing by spring 130.
A hydraulic valve mechanism 170 is provided at a rear end portion
of housing 110 for receiving oil under pressure from an external
oil supply source and accurately controlling the protrusion biasing
force of the plunger 120. This hydraulic valve mechanism 170
comprises a ball seat 171 press-fit into the housing 110, a check
ball 172 engageable with the ball seat 171, and a retainer 173 for
retaining the check ball 172. The valve mechanism permits the flow
of oil into a high pressure oil chamber 180 defined by plunger 120
and hole 111, but blocks reverse flow of oil from the high pressure
oil chamber 180, so that tension is imparted to, and maintained
smoothly in, the chain by plunger 120.
In the operation of the chain tensioner 100, when the timing chain
TC becomes loose, the plunger 120, biased by the protrusion biasing
spring 130, immediately moves in the protruding direction.
FIG. 4(a) shows the condition of the tensioner before the plunger
protrudes, FIG. 4(b) shows the tensioner as the plunger is moving
in the protruding direction, and FIG. 4(c) shows the plunger moved
forward by one tooth.
When the plunger 120 moves in the protruding direction to maintain
tension in the timing chain, the racks 121 on the plunger 120 draw
the cams 140, which are initially in the position shown in FIG.
4(a), in the protruding direction against the force applied to them
by the biasing spring 150. As the cams are drawn in the protruding
direction, a camming action exerted by the teeth of the racks,
which are in the shape of ratchet teeth causes the cams to slide
radially outward while in engagement with the tapered seats 112.
The cams simultaneously rise and move outward, while sliding on the
tapered seats, to a position where they become disengaged from the
rack teeth on the plunger, as shown in FIG. 4(b).
When the cams 140 rise on the tapered surfaces of the tapered cam
sliding seats 112 and the engagement with the racks 121 by the
plunger 120 is relieved, the plunger 120 moves forward by one
tooth. Spring 150 then immediately pushes cams 140 downward, that
is, in the direction of retraction of the plunger, as shown in FIG.
4(c), and the engagement between the cam teeth and the racks blocks
retraction of the plunger 120.
As shown in FIG. 5, the force F received by the plunger 120 is
split into forces f1 and f2, which are applied to the seats on
opposite sides of the plunger. Thus the load applied to the housing
110 is distributed so that concentration of the load is avoided.
Moreover, as mentioned previously, the load is distributed
symmetrically so that eccentricity is avoided.
When a traveling timing chain TC loosens, the plunger 120 is moved
forward sequentially, one tooth at a time, to impart proper chain
tension to the chain. At the same time, reverse movement of the
plunger is prevented so that proper chain tension can be
maintained. Although the housing 110 is made of aluminum in the
present example, localized wear of the kind which occurs in a
conventional housing is avoided. Moreover, a significant reduction
in the overall weight of the tensioner can be achieved.
The invention affords other significant benefits. Since a simple
cam support structure is used, in which a pair of cams 140 are
inserted into tapered recesses, the problem of achieving the high
manufacturing accuracy and high mounting accuracy required in the
case of a pivot pin and pin hole for pivotally supporting a pawl
are avoided. Moreover, the difficulties encountered in
manufacturing and assembling the ratchet pawl, and achieving
accuracy therein, are also avoided, and the working accuracy and
working load in the part working and the assembly working can be
reduced.
Furthermore, by using the protrusion biasing spring 130, interposed
between a front end of the plunger 120 and the spacer 160, to hold
the spacer 160 in abutting relationship with the front of the
housing, the cams 140 can be easily inserted into their recesses,
and a simple device configuration, and easy assembly thereof, can
be realized.
Because the two racks 121 are situated on opposite sides of the
plunger 120, the plunger can be rotated in the housing by 90
degrees to release the racks from the cams 140. Accordingly,
assembly can be carried out easily, and the engagement between the
racks and the cams can be released easily for maintenance or for
checking the timing chain.
The chain tensioner 200, according to a second embodiment of the
invention is shown in FIGS. 6 and 7. This tensioner is also an
outer attachment type tensioner, having the same structure as that
of the first embodiment. Accordingly, reference numbers in FIGS. 6
and 7 exceed the reference numbers designating corresponding
components in FIGS. 1-5 by 100.
In FIGS. 6 and 7, a protrusion biasing spring 230 is interposed
between the rear end of the plunger 220 and the bottom of
plunger-receiving hole 211. The spacer 260 is screwed to the front
end of the housing. That is, it may be secured to the front end of
the housing 210 by screw fasteners, or alternatively, it may be
threaded onto the front end of the housing. Many of the features of
operation and advantages of the second embodiment are substantially
the same as those of the first embodiment.
The tensioner 200 can be miniaturized by reducing the distance from
the front end of the plunger 220 to the front end of the housing
210. Moreover, the tensioner can be arranged nearer to the chain,
so that its response to changes in tension of the timing chain TC
can be improved. Additionally, in this embodiment, the plunger 220
is prevented from separating from the housing by the fact that the
spacer 260 is independently secured to the housing. Therefore
disengagement of the plunger from the housing is prevented.
In FIG. 8, tensioner 300, which is a third embodiment of the
invention, has the same basic structure as in the first embodiment.
Here, components are designated by reference numbers that exceed by
200 the reference numbers for corresponding components in FIGS.
1-5.
The chain tensioner 300 differs from the tensioner of the first
embodiment principally in that mounting holes 313 are provided for
mounting the chain tensioner 300 on an engine block inside the
engine, so that this tensioner is a "inner attachment" type
tensioner. Otherwise, the features of operation and advantages of
the third embodiment are substantially the same as those of the
first embodiment.
Although the chain tensioners have been were described as used with
a timing chain TC they can also be used with a timing belt.
Important advantages of the invention may be summarized as
follows.
The tensioner not only maintains proper chain tension but also
distributes the force exerted on the tensioner plunger by the chain
through both cams to the cam seats on opposite sides of the
plunger. Accordingly, localized wear of the housing, of the kind
generated in a conventional tensioner, is avoided. The invention
also results in an overall reduction in the weight of the
tensioner. In particular, because localized wear is reduced, the
housing, which accounts for most of the weight of a conventional
tensioner, can be formed of aluminum, and a significant weight
reduction can be realized.
Another important advantage is that the cam support structure, in
which a pair of cams are inserted into tapered recesses, avoids the
problems associated with the high accuracy requirements in the case
of a ratchet-type tensioner utilizing a pawl. Moreover, even if a
rack tooth or a pawl tooth is broken, exchange and maintenance can
be carried out quickly and easily.
The cam and rack mechanism in accordance with the invention can be
used advantageously in a tensioner having a hydraulic valve
mechanism for introducing oil from an external oil supply in order
to control the protrusion biasing force accurately. Accordingly,
proper chain tension can be imparted and maintained in a smooth
manner.
The invention has the further advantage that the racks and cams can
be easily disengaged by rotating the plunger. Accordingly, the
tensioner can be assembled easily, and can be disassembled easily
for maintenance of the tensioner or for checking or maintaining the
timing chain.
In the cases where the protrusion biasing spring is interposed
between the front end of the plunger and the spacer, handling of
the protrusion biasing spring is easy, and the spacer may be held
against the front of the housing by the spring without the need for
threads or fasteners.
In the second embodiment, in which the protrusion biasing spring is
interposed between the rear end of the plunger and the bottom of
the plunger-receiving hole, the distance from the front end of the
plunger to the front end of the housing can be reduced, and the
tensioner can be arranged nearer to the chain for improved
responsiveness to changes in tension in the chain.
In the second embodiment, since the spacer is independently secured
to the front end of the housing, the plunger can be more reliably
prevented from disengagement from the housing.
* * * * *